RESUMEN
BACKGROUND: Conditioned pain modulation (CPM) is a validated measure of the function of endogenous pain inhibitory pathways. Placebo effects reflect top-down inhibitory modulation of pain. CPM and placebo effects are both influenced by expectations, albeit to varying degrees, and are related to neurotransmitter systems such as the endogenous opioid system, and it can be speculated that CPM responses are positively associated with the magnitude of placebo effects. Yet, no studies have tested this. METHODS: The study included 19 patients with neuropathic pain. CPM was quantified as the difference in pressure pain threshold (PPT) as measured at the middle deltoid muscle before and after 5-min exposure to the cold pressor test (CPT) (conditioning pain stimulus). Placebo effects were tested via open and hidden applications of the pain-relieving agent lidocaine (2 mL) using a disinfection napkin controlled for no treatment. RESULTS: The mean (SD) PPT was 668.7 (295.7) kPa before and 742.3 (370.8) kPa after the CPT. The mean (SD) CPM response was -73.6 (214.0) kPa corresponding to an 11% increase in PPT, reflecting a normally functioning endogenous pain modulatory system. Large and significant placebo effects were observed in ongoing neuropathic pain intensity (p = 0.002). The CPM response did not predict the magnitude of the placebo effect (p = 0.765). Moreover, there were no interaction effects for the moderator variables: clinical pain level (p = 0.136), age (p = 0.347) and gender (p = 0.691). CONCLUSIONS: Conditioned pain modulation and placebo effects do not seem to be associated in patients with neuropathic pain. SIGNIFICANCE: Conditioned pain modulation and placebo effects are endogenous pain-modulating phenomena that are influenced by some of the same mechanisms. This study suggests that CPM and placebo effects in neuropathic pain are independent phenomena that may be mediated by different mechanisms.
Asunto(s)
Condicionamiento Psicológico/fisiología , Lidocaína/uso terapéutico , Neuralgia/fisiopatología , Umbral del Dolor/fisiología , Adulto , Anciano , Condicionamiento Psicológico/efectos de los fármacos , Femenino , Humanos , Lidocaína/administración & dosificación , Masculino , Persona de Mediana Edad , Neuralgia/tratamiento farmacológico , Dimensión del Dolor , Umbral del Dolor/efectos de los fármacos , Efecto Placebo , PresiónRESUMEN
BACKGROUND: Chronic oro-facial pain patients often perceive the painful face area as "swollen" without clinical signs, that is a perceptual distortion (PD). Local anaesthetic (LA) injections in healthy participants are also associated with PD. OBJECTIVE: The aim was to explore whether PD evoked by LA into the infraorbital region could be modulated by adding mechanical stimulation (MS) to the affected area. METHODS: Mechanical stimulation was given with a brush and a 128-mN von Frey filament. Firstly, sixty healthy participants were randomly divided into three groups: (i) LA control, (ii) LA with MS, (iii) isotonic solution (ISO) with MS as an additional control condition. To further examine the role of a multisensory modulation, an additional experiment was conducted. Twenty participants received LA with MS (filament) in addition to visual feedback of their distorted face. The results of the two experiments are presented together. RESULTS: All three LA groups experienced PD; per contra, PD was not reported in the ISO group. MS alone did not change the magnitude of PD: brush (P = .089), filament (P = .203). However, when the filament stimulation was combined with additional visual information of a distorted face, there was observable decrease in PD (P = .002). CONCLUSION: The findings indicate the importance of multisensory integration for PD and represent a significant step forward in the understanding of the factors that may influence this common condition. Future studies are encouraged to investigate further the cortical processing for possible implications for PD in pain management.
Asunto(s)
Anestésicos Locales/administración & dosificación , Potenciales Evocados , Cara/fisiopatología , Retroalimentación Sensorial/fisiología , Percepción del Dolor/fisiología , Distorsión de la Percepción/fisiología , Análisis de Varianza , Dolor Crónico/fisiopatología , Dolor Crónico/psicología , Cara/inervación , Dolor Facial/fisiopatología , Dolor Facial/psicología , Femenino , Voluntarios Sanos , Humanos , Masculino , Bloqueo Nervioso , Dimensión del Dolor , Reproducibilidad de los Resultados , Adulto JovenRESUMEN
Anecdotally, chronic oro-facial pain patients may perceive the painful face area as 'swollen'. Because there are no clinical signs, these self-reported 'illusions' may represent perceptual distortions and can be speculated to contribute to the maintenance of oro-facial pain. This descriptive study investigated whether chronic oro-facial pain patients experience perceptual distortions - a kind of body image disruption. Sixty patients were consecutively recruited to fill in questionnaires regarding i) pain experience, ii) self-reports of perceptual distortion and iii) psychological condition. Perceptual distortions were examined in the total group and in three diagnostic subgroups: i) painful post-traumatic trigeminal neuropathy (PPTN), ii) painful temporomandibular disorder (TMD) or iii) persistent idiopathic facial pain (PIFP). A large proportion of oro-facial pain patients reported perceptual distortions of the face (55·0%). In the diagnostic subgroups, perceptual distortions were most pronounced in PPTN patients (81·5%) but with no significant group differences. In the total group of chronic oro-facial pain patients, the present pain intensity explained 16·9% of the variance in magnitude of the perceptual distortions (R(2) = 16·9, F(31) = 6·3, P = 0·017). This study demonstrates that many chronic oro-facial pain patients may experience perceptual distortions. Future studies may clarify the mechanisms underlying perceptual distortions, which may point towards new complementary strategies for the management of chronic oro-facial pain.